An antisense approach is commonly utilized to block the expression of specific genes within cells. See, e.g., R. W. Wagner, Nature 372, 333-335 (1994); and W. Risau, PCT International Publication Number: WO95/13387 (1995). It is hypothesized that RNase H hydrolyses the RNA strand of a RNA-DNA duplex and is likely to be responsible for the antisense effects of 2'-deoxyoligonucleotides. The translation initiation site of a mRNA is often used as the antisense binding site on the assumption that this region is important and accessible. However, recent studies such as those of Risau, supra, indicate that most regions of the mRNA are in fact accessible to oligonucleotides, except for those with strong secondary structure.
It has been shown that the carboxyl terminus (C-terminus) of the erythropoietin receptor (EPOR) is a negative regulation domain for cell growth. See James Ihle et al., Bailliere's Clinical Haemotology 7, 17-48 (1994); and A. D. DeAndrea et al., Mol Cell Biol. 11, 1980-1987 (1991). Further, this view is supported by the following evidence:
(i) In EPOR transfectants of Ba/F3 cells, a 40 amino acid truncation at the C-terminus enhances cell proliferation (DeAndrea et al., supra).
(ii) In a naturally occurring human EPOR mutant, a 70 amino acid truncation at the C-terminus caused erythrocytosis. The affected individuals have excellent or superior health without abnormalities (A. D. L Chapelle et al., Proc. Natl. Acad. Sci. USA 90, 4495-4499 (1993)).
(iii) Hematopoietic cell phosphatase (HCP), which down regulates the EPO-induced cell proliferation, binds to a region close to the C-terminus of EPOR (Taolin Yi et al., Blood 85, 87-95 (1995)).